The present invention pertains to a colloidal silica-based composition that affords low defectivity levels when used as a component in chemical mechanical planarization (chemical mechanical polishing, CMP), and especially for oxide CMP.
Chemical mechanical planarization (chemical mechanical polishing, CMP) is now widely known to those skilled in the art and has been described in numerous patents and open literature publications. Some introductory references on CMP are as follows: “Polishing Surfaces for Integrated Circuits”, by B. L. Mueller and J. S. Steckenrider, Chemtech, February, 1998, pages 38–46; and H. Landis et al., Thin Solids Films, 220 (1992), page 1.
In a typical CMP process, a substrate (e.g., a wafer) is placed in contact with a rotating polishing pad attached to a platen. A CMP slurry, typically an abrasive and chemically reactive mixture, is supplied to the pad during CMP processing of the substrate. During the CMP process, the pad (fixed to the platen) and substrate are rotated while a wafer carrier system or polishing head applies pressure (downward force) against the substrate. The slurry accomplishes the planarization (polishing) process by chemically and mechanically interacting with the substrate film being planarized due to the effect of the rotational movement of the pad relative to the substrate. Polishing is continued in this manner until the desired film on the substrate is removed with the usual objective being to effectively planarize the substrate (both metallic and dielectric portions).
In oxide CMP a slurry is used to planarize films comprised of oxide dielectric material (e.g., silicon dioxide). In shallow trench isolation (STI) CMP a slurry is used to planarize structures comprised of oxide dielectric material and silicon nitride. Furthermore, it is desired that the oxide CMP and STI CMP slurry compositions and associated methods afford planarized substrates characterized to have low defectivity levels, low haze levels, and low levels of scratching.
During oxide CMP and STI CMP, considerable amounts of particles are generated from the abraded substrate materials as debris during the planarization process. These particles, in addition to undersized abrasive particles present in the CMP slurry, are high energy and may adhere to the planarized wafer oxide layer as contaminant causing defects. The particles generated from the abraded substrate materials, in addition to oversized abrasive particles present in the CMP slurry, may cause undesirable scratching on the polished/planarized oxide surface. Therefore, it is desirable to prevent debris particles generated during polishing from the abraded substrate materials, from adhering too strongly to the planarized oxide surface.
Oxide CMP compositions comprise an abrasive(s), which is very often colloidal silica. Colloidal silica is an effective and preferred abrasive for use in CMP (e.g., oxide CMP) in most respects but most or all colloidal silicas known in the art do possess one significant drawback. This drawback is that use of colloidal silicas, when formulated into polishing compositions for CMP, can afford relatively high defectivity levels, especially during oxide CMP.
More specifically, colloidal silica dispersions are often used in oxide CMP formulations for planarizing oxide dielectrics during the fabrication of IC chips. CMP processors using colloidal silica often observe high defectivity while using colloidal silica in their oxide CMP process. After polishing an oxide wafer with a colloidal silica-based slurry, defects usually appear as scratches and/or micro-scratches on the wafer surface. The scratches and micro-scratches can be counted and otherwise characterized directly without pretreating the polished oxide surface using optical metrology test methods. In addition, in order to count and otherwise characterize micro-scratches, the polished oxide surface is typically first dipped in hydrofluoric acid solution before doing optical metrology. The high defectivity levels observed on polished wafers subsequent to oxide CMP with a colloidal silica-based slurry correspond to yield loss and are therefore undesirable.
There is a significant need in CMP processing for colloidal silicas that afford low defectivity levels when used as component(s) in CMP slurries. The present invention provides a solution to this significant need.